Intramuscular diaphragm pacing stimulation (DPS) has been shown to be a viable therapeutic technique for replacement of chronic mechanical ventilation in patients with respiratory insufficiency, such as high-level spinal cord injury. DPS has also been demonstrated to have a clinically relevant effect in conditioning the diaphragm of patients with amyotrophic lateral sclerosis. These therapeutic applications of electrodes are ones in which the electrode are typically designed to be implanted for duration of the life of the patient or until mechanical failure of the electrode. Therefore, the electrodes are typically constructed with significant redundancy, reinforcement, and barbing to promote longevity and stabilization in the target muscle.
Some intramuscular electrodes have been developed for shorter-term applications. For example, intramuscular, percutaneous, single-helix design electrodes have been used for functional electrical stimulation in applications where the electrode is placed through a percutaneous needle insertion into the target muscle. These electrodes are typically removed by pulling axially on the electrode lead. However, the barbs on the electrodes, as well as fibrosis and encapsulation of the electrode by the surrounding tissue, frequently resist or complicate removal of the electrodes. The electrodes and/or the wires extending proximally from them therefore frequently break during removal, thus leaving the electrode or a portion thereof in the muscle or subcutaneous tissue, as well as creating an undesirable level of tissue disturbance. See Peterson et al., “Long-Term Intramuscular Electrical Activation of the Phrenic Nerve: Safety and Reliability,” IEEE Trans Biomed. Eng., vol. 41, no. 12 pp. 1115-26 (December 1994).
A number of design features are desirable in intramuscular electrodes that have not yet been fully met by available products. Most basically, intramuscular electrodes need to meet the design criteria of being able to deliver the desired level of stimulus to target tissue, and be able to mechanically survive such use. If extraction of the electrode is necessary, it is an advantage for the electrode to survive extraction without breaking apart and generating “unretrieved device fragments” (UDFs). UDFs are a serious hazard; the FDA health notifications report about 1000 adverse events per year that are related to UDFs. Additionally, the extraction undesirably and almost inevitably visits at least some trauma upon the target tissue. Data have shown that extractions of simple intramuscular helical electrodes (Case Western Reserve University type) result in a fracture rate of 53% of electrodes with known status of integrity recorded (Knutson et al., “Electrode fracture rates and occurrences of infection and granuloma associated with percutaneous intramuscular electrodes in upper-limb functional electrical stimulation applications,” J. Rehab. Res. & Dev., vol. 39, no. 6, pp. 671-83 (November/December 2002)). See also Bhadra et al., “Extraction Force and Tissue Change During Removal of a Tined Intramuscular Electrode from Rat Gastrocnemius,” Ann. Biomed. Eng., vol. 34, no. 6, pp. 1042-50 (June 2006).